Z/W Axis summing with scale on Z axis

[CRM]

We have a Centroid knee mill retrofit at work that utilizes the MPU11 & GPIO4D hardware to control 3rd party DC drives and running CNC12 software. The mill has glass scales on BOTH the knee and the quill. We specifically asked that it be configured for axis summing of the Z (quill) and W (knee). The company that did the retrofit has been difficult to work with regarding what I consider some configuration problems.
Currently, the mill is configured with FIVE DROs: X axis, Y axis, ZW axis, W axis, and M (manual quill icon) axis. The technician from the retrofit company claims it must be this way in order to have both the "smart Z" and Z/W axis summing functions. I don't understand why I can't just have 4 DROs: X, Y, ZW, and W.
Anyone with an Elrod CNC quill conversion knows it's not the most rigid way to couple the quill to a servo leadscrew, and results in higher backlash and lost motion than the X & Y axes. Why aren't we able to use the glass scale on the Quill for servo position feedback AND position display, instead of only as the input signal for the (manual axis) quill position display when the leadscrew is uncoupled from the quill? Right now, the servo's rotary encoder is used for summing the Z & W axes (as well as the servo position closed loop that the MPU11 needs) And since the servo position feedback is taken from the servo motor shaft, I'm seeing .003"-.005" backlash error at the spindle when using an indicator to check movement. Isn't the point of glass scale position feedback to significantly reduce that? I read thru the post Re: ALLIN1DC and ENCEXP scale configuration (Answered) and as far as I understand we should not even need the motor encoder input. Am I mistaken?
Encoder inputs are as follows:
input#1 X axis servo rotary encoder
input#2 Y axis servo rotary encoder
input#3 Z axis (quill) servo rotary encoder
input#4 W axis (knee) glass scale
input#5 Z axis (quill) glass scale
I have also attached a current system report.

[tblough]

You CAN use the Z-axis scale for feedback. You just need the Mill Ultimate software. You will get duplicate encoder messages when you exit machine setup, but you can ignore those.